The present invention relates to a pressurized fluid operated shifting mechanism for cooperation with a shift bar housing assembly for selectively shifting a change-gear mechanical transmission. More particularly, the present invention relates to such a fluid operated shifting mechanism of the "X--Y" type, and will be described in connection therewith.
Shift bar housing assemblies for change-gear mechanical transmissions typically comprise a plurality of generally parallel, independently axially movable shift bars or shift rails, each carrying a shift fork fixed thereto. Each shift bar or shift rail may be selected and moved axially to effect engagement/disengagement of a particular gear ratio. Such assemblies are well known in the prior art and may be better understood by reference to U.S. Pat. Nos. 4,455,883; 4,575,029; and 4,584,895, all of which are incorporated herein by reference.
Such shift bar housings may be manually controlled by the vehicle operator, by means of a shift lever. More recently, it is becoming increasingly popular to utilize automatically controlled pressurized fluid actuating shift-actuators with such shift bar housings. In a pressurized fluid operated shift-actuator, a shift finger is automatically moved in the X--X (rail selection) direction, in response to actuation of one fluid pressure device, then the shift finger is automatically moved in the Y--Y (gear engagement/disengagement) direction in response to actuation of another fluid operated device.
Shift bar housing assemblies utilizing pressure operated shift-actuators to control each shift rail in an automatic or semi-automatic mechanical transmission are known in the prior art, as may be better understood by reference to U.S. Pat. Nos. 4,445,393, 4,722, 237, and 4,928,544 all of which are incorporated herein by reference.
The prior art fluid operated shift-actuators for providing automatic and/or semi-automatic rail selection of change gear mechanical transmissions were generally satisfactory for use with transmissions including only three shift rails (i.e., five forward speeds plus reverse). However, it has become quite desirable to be able to achieve automatic and/or semi-automatic rail selection and shifting of transmissions having four shift rails (i.e., seven forward speeds plus reverse). See for example U.S. Pat. No. 4,388,838, assigned to the assignee of the present invention and incorporated herein by reference. For such transmissions, the known fluid pressure operated shift-actuator for moving the shift finger in the X--X (rail selection) direction, is not commercially available, and is not known in the prior art.